The invention relates to a cutter insert for milling tools, particularly corner milling cutters, as well as a milling tool provided with such a cutter insert.
As a rule, milling tools are provided with cutter inserts which may be secured in their respective insert seat in several orientations. In this manner several cutting edges provided on the cutter insert may become active in succession, whereby the service life of the cutter insert is extended. The geometrical configuration of a cutter insert significantly affects the chip formation. For example, in most cases a positive rake angle is desired, both at the peripheral cutting edges and at the frontal cutting edges of a milling tool. As a rule, these desiderata are taken into account in the shaping of the cutter insert. “Positive cutter inserts” have at their cutting edges wedge angles which are significantly less than 90°. Such a result is achieved by ensuring a suitable inclination of the side surfaces (free surfaces) and the top surface (rake surface).
Such cutter inserts are described, for example, in German patent document DE 36 18 574 A1 corresponding to U.S. Pat. No. 4,699,549. The rake surface of such a cutter insert, as illustrated, for example, in FIGS. 42, 55 and 56 of that document, differs from the shape of a simple plane. The rake surface is formed of two partial surfaces which slope downward toward a diagonal intersecting the securing opening. The base surface of such cutter inserts is planar. The insert seat of the tool body accordingly has a planar conforming engagement surface.
Reversible cutter inserts of the above-outlined conventional construction may be secured in two different orientations in their respective insert seat. The positions of the insert differ from one another by a rotation through 180° about an imaginary axis passing coaxially through the securing opening. In case the cutting edges accessible in either positions have become worn, the cutter insert must be replaced as a whole.
It is accordingly the object of the invention to provide a cutter insert and a milling tool therefor, wherein the cutter insert has an improved useful life.